This outtake footage is strange. It is actually from the UK Thames TV show "This is your life". Thames also produced MATH and they did a segment called "Richard O'Sullivan this is your life" and that is the title of the YT video where you can find the rehearsal film.

Remember both TV shows were made down the hall from one another at Thames. O'Sullivan goes to film a scene from a MATH ep called 'The Tender Trap' when the TIYL announcer walks up from behind him, and surprises Richard and tells him the TIYL ep is about him.